In recent years, the so-called organic thin-film transistors, in which semiconductors composed of organic materials are used, have been attracting attention over inorganic semiconductors such as silicon.
In recent years, there have been reports on examples of organic thin-film transistors that exhibit the same mobility as amorphous silicone thin-film transistors (a-Si TFTs) do. Further, the capability to produce elements at a low processing temperature of not more than 200° C. has made it possible to form transistor elements on lowly heat-resistant plastic substrates and the like. Thus, studies have been conducted on techniques for realizing flexible devices with use of the flexibility of plastic substrates.
Further, the organic materials allow production of devices through print processes and the like, depending on types of material. As such, the organic materials are expected to serve as semiconductor elements that allow a reduction in manufacturing cost and manufacture of large-area devices by printing.
In terms of putting transistors to practical use, it is important to control current-voltage characteristics. Above all, in terms of operating transistors within a desired voltage range, it is extremely important to control a threshold voltage characteristic.
For example, Non-Patent Literature 1 discloses a method for controlling a threshold voltage characteristic by forming an organic silane compound layer between a gate insulating film surface and an organic semiconductor layer.
Further, Patent Literature 1 discloses a method for controlling the threshold voltage by forming silane compound layers between a source electrode and an organic semiconductor layer, between a drain electrode and the organic semiconductor layer, and between a gate insulating film and the organic semiconductor layer, respectively.
Patent Literature 1 also discloses forming layers of an fluoroalkylthiol compound (F17C10-Thiol) between the source electrode and the organic semiconductor layer and between the drain electrode and the organic semiconductor layer (on the source and drain electrodes), respectively.